Method of treating nylon bristles and products produced thereby



Claims. (Cl. 117138.5)

The present invention is concerned with improvements in the art of treating filaments of nylon and, in particular, to the treatment of nylon bristles of the type employed in tooth brushes and the like.

Nylon bristles have, to a large extent, replaced animal bristles in the manufacture of tooth brushes. While the strength and cleanability of the nylon bristles are excellent, such bristles havethe disadvantage that they may support bacterial growth.

Attempts in the past to render nylon bristles self-sterilizing, have not always proven successful. A substantial amount of development work in this connection has made use of various phenyl mercury compounds, particularly phenyl mercury salts, as agents for rendering the bristles bacteriostatic. In many cases, the phenyl mercury compound, because of its extremely limited solubility in Water, tad to be applied as a suspension. This method of application was not particularly successful because of the difficulty in securing a uniform, adherent deposit of the agent upon the surfaces of the bristles.

In order to overcome this difficulty, it was suggested that the phenyl mercury salt be dissolved in a relatively strong acid prior to application to the nylon bristles. This procedure, too, had its disadvantages. Hydrochloric acid was found to be substantially useless for this purpose because the addition of the acid to the phenyl mercury salt precipitated the very insoluble chloride. Some use was made of concentrated nitric acid, but this procedure had the disadvantage of discolor-lug and softening the bristles to the extent that they became limp and substantially useless for the intended purpose.

With the foregoing in mind, an object of the present invention is to provide an improved method for rendering nylon filaments, particularly bristles, bacteriostatic.

Another object of the invention is to provide an improved rnethod for treating nylon bristles and the like with phenyl mercury compounds under conditions such that the phenyl mercury compound will become tightly bonded to the nylon bristles.

Another object of the invention is to provide an improved composition for conditioning and treating nylon bristles with phenyl mercury compounds in order to render the bristles bacteriostatic.

Still another object of the invention is to provide an improved tooth brush consisting of nylon bristles having bonded thereto, or absorbed thereon, an active bacteriocidal agent.

The foregoing objects are achieved in the practice of the present invention through the discovery that boric acid effectively cooperates with pl'i enyl mercury compounds in conditioning nylon filaments such as bristles for the reception of the phenyl mercury compound as a tightly adherent, active bacteriostatic coating or impregnating deposit. The advantages to be realized from the combination of the phenyl mercury compound and boric acid include (i) an absence of discoloration on the nylon bristles; (2) absence of any objectionable odor of the type which may be encountered, for example, through the use of volatile acids such as acetic or formic acids; (3) the ability to produce a clear solution for impregnating or coating the nylon bristles, rather than a suspension; and (4) the ability to provide a tightly adherent coating which 2,836,516 Patented May 27, 1958 does not lose its bacteriostatic properties even after repeated scrubbings.

More particularly, the nylon filaments are given a bacteriostatic coating by immersing the same in a clear aqueous solution containing, for every 190 milliliters of water, from to milliliters of a Water soluble alcohol having from 1 to 4 carbon atoms per molecule, from 4 to 10 grams of a phenyl mercuric compound which is soluble at least to that extent under the pH conditions prevailing in the solution, and at least 2.0 grams of boric acid.

While the manner in which the boric acid acts to improve the characteristics of the resultant coating is not clear, it appears that the boric acid has the property of conditioning the nylon fibers either by a surface reaction, or by some other mechanism, for the reception of the phenyl mercuric compound. This conditioning is achieved without making the fibers limp, discoloring them, or otherwise injuring the filaments.

As another possible explanation, the boric acid may react with the phenyl mercuric compound to form a borate which is subsequently deposited on the nylon filaments and has the abilty to adhere tightly thereto.

Whatever the mechanism, it has been established that the combination of boric acid with the phenyl mercuric salt does provide improved results over the use of various other phenyl mercuric salt combinations previously suggested.

The type of nylon bristles which may be treated in accordance with the present invention is not particularly critical, since the process has been successfully applied to the treatment of type 66 nylon, which is a polymerized hexamethylene diamine adipate, and to type 610 nylon, which is hexamethylene diamine sebacate.

The procedure involved in applying the solution to the bristles is quite simple. In the case of a tooth brush, the entire head and, if desired, the stem of the brush is immersed in the solution, while the solution is maintained at a temperature of at least 50 C. Normally, a few minutes immersion will suffice. After immersion, the filaments are dried, preferably at about 60 C., followed by a number of rinsings in water to remove the water soluble material. 'The deposit or coating which remains evidences no odor of acetic acid or other volatile acid.

In testing the bacteriostatic properties of the treated bristles, the method described in FDA circular No. 198 was employed. In this test, a nutrient agar is seeded with Micrococcus pyogenes var. aureus. The bristle or bristles to be tested is placed within the agar and incubated for a period of about 48 hours. The zone of inhibition, in which there is no growth of the bacteria is measured with a rul r at various points about the bristle. Any zone of inhibition whatever is considered satisfactory, and an inhibited zone of two millimeters or more is considered excellent.

The following specific examples illustrate the treatment of the present invention, and the results obtained.

Example I A clear solution was made up at a temperature of about 60 C., including 50 milliliters of water, 50 milliliters of ethyl alcohol, 3.0 grams of phenyl mercuric acetate, and 1.7 grams of boric acid. in the place of the phenyl mercuric acetate, there may be employed any phenyl mercuric compound which has a reasonable solubility at the pH of the solution. For example phenyl mercuric nitrate, phenyl mercuric lactate, or phenyl mercuric hydroxide may be employed.

Three specimens were dipped into this solution. One consisted of a single bristle formed into a loop exactly as it would be in the head of a tooth brush. The second sample consisted of a set of four bristles in a tuft, and the third consisted of an entire tooth brush head.

. 3 Each of the specimens was immersed in the solution for a period of minutes at a temperature of 70 C. After immersion, the specimens weredried for 60 minutes at.60 C., followed by three rinsings in water.

The ability of the coating and/or impregnation to remain active on the surface of the nylon bristles was determined in the following manner. be tested was fastened onto a clamp of a machine that has a reciprocal motion such that the brush head travels back and forth about 2 inches during each stroke at a rate of about 150 strokes per minute. The weight applied to the brush head was 100 grams. The brush head, during reciprocation, is pressed 'by such weight against a series of glass rods which are spaced about a quarter of an inch apart and are one-quarter inch in diameter; The reciprocating motion thereby scrubs the The brush to v bristle ends against the glass rods much as the ends" would be scrubbed against teeth. The brush is wetted when the machine is started with a one inch length of tooth paste.- Additional amounts of tooth paste are added every minutes. During the brushing or scrubbing operation, the brush is always immersed in .a foamy solution of tooth paste. Normally, the brush is, operated in the machine for an 8 hour period and then removed and leached in running water at room temperature or slightly below overnight, followed by more brushings.

After this type of abrasion test, a single bristle when tested in the above described bacteriostatic activity test exhibited a very small zone of bacteriostatic activity immediately at the tip of the bristle, andbacteriostatic zones measuring two millimeters .at the sides of the bristle and at the bight of the loop. With the four bristle tuft, there was an area measuring about one-half millimeter in diameter at the tip of the bristles, a'.zone of three millimeters at the sides of the bristle, and one of three millimeters ,thiclgness at the bight. When the entire head was tested in the same manner, the bristles evidenced a 'bacteriostatic inhibition extending'forseven millimeters beyond the head, and for twelve millimeters beyond the handle portion of the brush.

When the same bacteriostatic activity test was applied to a tooth brush which had undergone 59,500 scrubbings, the single bristle from the brush still evidenced a satisfactory amount of bacteriostatic activity. At the tip' of the bristle, there was a zone of 0.5 millimeter in which the growth of the bacteria was static. Along the sides of the bristle, the zone extended to about onhiillimeter and at the bight, it extended to about 0.5 millimeter. For the four bristle tuft, the corresponding values were one millimeter at the tip of the bristles, three millimeters at the sides, and three millimeters at the bight.

Example II static activity at the tip and at the bight, and a bacteriostatic zone of two millimeters extending from the sides of the bristle. A tuft of four bristles had a bacteriostatic zone of 0.5 millimeter at the tip, five milli meters at the bight, and three millimeters along the sides of the bristles.

An ordinary tooth brush head contains about one gram of nylon in the bristles. With the composition employed in the present invention, the nylon bristles are capable V of holding a suficient amount of the mercuric salt to provide a content of mercury in the range from about one to three milligrams per gram of nylon.

From the foregoing, it will be appreciated that the com- 7 V a position and method 'of the present invention provide an improved bacteriostatic nylon filament, particularly effective as a tooth brush bristle, having the advantages of long lasting effect, lack of odor, lack of discoloration, and ease of application.

It Will be evident that various modifications can be made to the described embodiment without departing from the scope of the present invention. I

We claim as our invention: a

1. The method of rendering nylon filaments bacteriostatic for use in tooth brushes which comprises dipping said filaments into an aqueous solution containing, forevery 100 milliliters of water, from 80 to 120 milliliters of a water soluble alcohol, from 4 to 10 grams of a phenyl mercuric compound selected from the group con-.

said filaments into an aqueous solution containing for everyjlOO milliliters of water, from780 to 120 milliliters of a water soluble: alcohol, from 4 to 10 grams of a phenyl mercuric compound selected from the group con:

sisting of phenyl mercuric acetate, phenyl mercuric nitrate, phenyl mercuric lactate and phenyl mercuric hydroxide, dissolved insaid solution, and at least 2.0 grams of boric acid, said solution being at a temperature of at least 50 C., and thereafter drying said filaments.

' 3. A method of rendering nylon filaments bacteriostatic for use in tooth brushes which comprises dipping said filaments into an aqueous solution containing, for

'every milliliters of water, from 80 to milliliters of a wat'ersoluble alcohol, from 4 to 10 grams of a phenyl mercuric compound selected from the group consisting of phenyl mercuric acetate, phenyl mercuric nitrate, phenyl mercuric lactate and phenyl mercuric'hydroxide, soluble in said aqueous solution, and at least 2.0 gramsof boric acid, thereafter drying said filaments, and repeatedly rinsing the dried filaments in water.

4, The method of rendering nylonfilaments bacteriostatic for use in tooth brushes which comprises dipping said filaments into an aqueous alcohol solution consisting essentially of water, a water soluble alcohol, a phenyl mercuric compound selected from the group consisting of phenyl mercuric acetate, phenyl mercuric nitrate, phenyl mercuric lactate and phenyl mercuric hydroxide, and boric acid, the proportions being for every 100 milliliters of water, 80 to 100 milliliters of water soluble alcohol, 4 to 10 grams of a soluble, phenyl mercuric compound and at least 2.0 grams of boric acid, maintain ing said solution at a temperature of at least50 C.,

immersing the filaments in said solution for at least a V few minutes, removing said filaments from said solution; drying said filaments, and then rinsing the bristles in water.

5. Bacteriostatic nylon filaments for'tooth brushes produced according to the method of claim 4 which contain from 0.1 to 0.3% of mercury based upon the weight of nylon.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Rayon andSynthet-ic Textiles, vol. 31, No. 5, 1950, p. 91.

May 

1. THE METHOD OF RENDERING NYLON FILAMENTS BACTERIOSTATIC FOR USE IN TOOTH BRUSHES WHICH COMPRISES DIPPING SAID FILAMENTS INTO AN AQUEOUS SOLUTION CONTAINING, FOR EVERY 100 MILLILITERS OF WATER, FROM 80 TO 120 MILLILETERS OF A WATER SOLUBLE ALCOHOL, FROM 4 TO 10 GRAMS OF A PHENYL MERCURIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHENYL MERCURIC ACETATE, PHENYL MERCURIC NITRATE, PHENYL MERCURIC LACTATE AND PHENYL MERCURIC HYDROXIDE, DISSOLVED IN SAID SOLUTION, AND AT LEAST 2.0 GRAMS OF BORIC ACID, AND THEREAFTER DRYING SAID FILAMENTS. 